It has long been known that the strength of a circular concrete tank can be substantially increased by wrapping the tank with many turns of flexible, high strength wire.
There are basically two types of wire wrapping machines in use today. One of these types of machines is commonly referred to as wall hung. Although that type of machine is not the subject of this invention, it nevertheless is appropriate to mention that a machine of this first type is suspended from the top of the tank. During wire wrapping of the tank, the top of the wall of the tank is utilized as support, with this type of machine, also known as a wire guide, moving in a circle around the tank for numerous turns as the tank is being wrapped.
These devices are typically propelled by a chain that is wrapped around the structure. Although accurate, these machines are typically very slow, not only in speed of travel around the structure, but also time is consumed at the time the operator must effect a changeover from one roll of wire to the next. In addition, these wall hung machines are very expensive to own, it is reported that a new one costs in the neighborhood of $130,000.00. Furthermore, in addition to being expensive, these machines are complex to operate and require the stocking of replacement parts of a specialty nature.
Not only is highly skilled and therefore expensive labor involved, but also these wall hung machines require a long set up time. For example, it would be correct to say that on a smaller size tank, a wire wrapping machine that travels on the ground surface around the tank can be set up, the pre-stressed wire wrapped around the structure, and thereafter dismounted before the wall hung machine can ever be set up and placed in operation.
Although many patents have been granted on wall hung machines, it should be sufficient to mention that the Bush et al Pat. No. 4,801,103 which issued Jan. 31, 1989 exemplifies this type of device.
A different type of machine for achieving basically the same result is the so-called ground running machine, with this type of machine being the subject of the present invention. A typical machine of this type consists of a platform, a prime mover or another type of propulsion, a wire roll, wire stressing assembly, tension gauge, and payoff wheel. The machine is towed around the tank a large number of times, with each revolution of the machine serving to place another turn of wire around the tank. These turns are sometimes referred to as wraps of wire.
In order to meaningfully increase the strength of the tank being wrapped, it is necessary to maintain a substantial tension in the wire. For this reason, the wire leaving the wire roll thereafter passes through a wire stressing assembly used to assure that a proper tension will be provided to the wire as it is being wrapped around the tank. Hydraulic pressure is typically utilized for applying a substantial force to a slipbrake operatively associated with the wire stressing assembly. A hydraulic pump under the control of the operator makes it possible for the hydraulic pressure to the wire stressing assembly to be altered as necessary in order to maintain a proper and consistent tension in the wire. In some instances pneumatically operated components could be utilized instead of hydraulically powered components.
It is customary to provide a gauge placed for easy viewing by the operator so that he can ascertain the tension of the wire being wrapped around the large structure. The operator adjusts the pressure applied by the slipbrake by increasing or decreasing the hydraulic pressure, which causes the slipbrake to increase or decrease the tension in the wire. The gauge viewed by the operator typically is equipped with a needle, with this needle often varying rapidly because the ground surface over which the machine is traveling is usually not perfect and uniform. Because of the non-uniformity of the roadway circling the tank, often accompanied by some variation in speed of the towing vehicle, the needle of the gauge frequently reflects an undesirable variation in wire tension, which may run as high as 10%.
Typically the wire wrapping procedure starts by securing an end of the wire on the roll, threading this end of the wire through the machine, and then attaching it to the structure of the circular prestressed concrete tank. Usually a bolt is drilled into the wall of the tank with the end of the wire attached to the bolt. In most instances, the wire wrapping procedure commences at the bottom of the tank, with the wrap proceeding in a consistent, helical manner toward the top.
It is of interest to note that there are two sizes of wire customarily used, with one of these being an 8 gauge wire (0.162" in diameter), which is typically tensioned at 3,000 pounds.
Also used is a somewhat larger 6 gauge wire (0.192" diameter), that is typically tensioned at 4,250 pounds. As is known, the breaking strength of wire is 60% above the normal operating tension.
A roll of wire will weigh between 600 pounds and 2,000 pounds, depending on availability and preference. Approximately 13 lineal feet of 8 gauge wire weighs one pound, whereas approximately 9 lineal feet of 6 gauge wire weighs one pound. From this it can be seen that the capacity of a roll of wire can be readily calculated and generally speaking, the typical roll of wire will enable a tank to be wrapped for 20 to 60 turns, depending on the size of the tank and the size the roll of wire.
It should be mentioned in passing that in some instances it is desirable for more than one layer of wire to be placed on the structure. After the first layer has been wrapped, it is typical to apply a layer of concrete over this first layer in order to encapsulate the wire. Thereafter a second wire wrap may be applied to the structure. Although it is possible with the present equipment to wrap from the upper part of the tank downwardly, it is typical to start again at the bottom of the tank and then wrap in an upward manner.
The wire unrolled off of the roll of wire passes through a pretensioner, which may take the form of two blocks of steel utilized in conjunction with an adjustable hydraulic cylinder, with the wire extending between these two blocks. The hydraulic cylinder enables the operator to select the amount of force with which the blocks of steel are caused to be moved together, with the squeezing of the wire that passes between the two pieces of steel creating a substantial amount of friction and a desirable amount of initial tension in the wire.
The wire is then wrapped around a rotatable component known as a capstan for a suitable number of times, such as seven times, with the wire then passing over a nearby payoff wheel before being wrapped around the tank. It is customary to travel around the tank in what may be regarded as a clockwise motion, but this is of course not a firm requirement. Once the wrapping has started, it is understood that the wrapping will proceed continuously around the tank until almost all the wire on the roll has been expended. The machine is then stopped and the end of the wire is clamped.
A special clamp, well known in the industry, is used for securely fastening wires, usually two, together. The type of clamp I prefer involves a pair of similarly sized plates, each provided with three or more spaced parallel grooves. One of these plates is inserted under two of the wires previously wrapped upon the tank, with those wires residing in the grooves of that plate. Then the second plate is placed atop the first plate, with the same wires residing in the grooves of the top plate, at which time the plates are bolted tightly together. When the tension is let off of the now-expended roll, the clamp tightly maintains the tension of the wires previously placed. This type of clamp serves the additional purpose of preventing the entire structure from unwrapping in the event that a break in the wire occurs.
To be noted in passing is the fact that in the event of a break, the wire will become slack only as far back as the previous clamp. It then becomes necessary to remove all the slack wire and throw it away, with the wrapping procedure to start again from the last point where the wire was tight.
When the new roll of wire has been placed in the operational location, the end of this new roll is then made available, with the two ends of the wires being spliced together. This is typically accomplished by the use of a spiral splice that is well known in the industry, although it is always possible to weld the ends of the two wire together. It is usually preferable to use a splice because it is simple, quick, easy and effective.
After the ends of the wires have been secured together, the wire wrapping procedure starts up again and continues until the next roll has been fully expended or nearly expended, with another roll then being added and the procedure continued until the structure has been fully wrapped. On a larger size structure, this may require the utilization of over 100 miles of properly tensioned wire.
It is to be noted that a skilled operator of this type of machine can bring about the tensioning of the wire to within 5% of the desired tension reading by carefully watching the fluctuations of the needle utilized to indicate wire tension. Typically the needle will fluctuate from the upper limit to the lower limit about once every two seconds. Despite the skill of the operator and his conscientious efforts to carefully control wire tension, one of the problems of this arrangement is that the tension gauge is not mounted and calibrated to accurately read the tension in the wire. Typically the tension gauge will read about 80% to 35% of the actual tension in the wire. This causes problems inasmuch as the operator has to compensate for this inadequacy by conjecturing as to the actual tension in the wire as he notes the tension shown on the tension gauge.
Still another problem is involved in the fact that when the wire is being wrapped around a relatively low part of the structure, the gauge will read higher than when the wire is being applied to the upper portion of the structure, this being true despite the fact that in both instances, the actual wire tension is the same.
To compensate for the difference between the tension shown on the tension gauge and the actual wire tension, it has been necessary, in accordance with known prior art procedures, for the workmen to take certain steps in order to assure that the tension on the structure is per design.
A first of these known procedures involves slopping the operation periodically and measuring actual wire tension on the structure. To accomplish this, a portion of the wire is pulled off of the structure and a special gauge is placed on the wire that will show the tension in the wire. This type of gauge is called a tensiometer or stressometer and is quite familiar to those working in this field. This procedure is known as "reading the wire." Once the actual tension of the wire on the wall has been read, this information is relayed to the operator. This enables the operator to calibrate his equipment, making an adjustment in hydraulic pressure, either up or down, in order to assure that the wire tension on the wall will be consistent with a desired value.
A second of the well known procedures to which the workmen may resort in an effort to assure proper and consistent wire tension involves measuring and recording the tension in each wire on the wall. The workmen will pick one point on the wall that is typical and they will read and log the tension in each wire on the wall at that location. The workmen will then add up the tension in these wires and determine if additional wire needs to be placed on the wall. If the total tension is below design, then additional wraps will be authorized.
Although these procedures have proven effective over the years, considerable improvement is needed, particularly in view of the fact that it is expensive in terms of labor and time to have to stop the wrapping procedure in order to read the wires and log them. In addition, it is quite expensive in terms of labor, time and materials should it become necessary to add more wire wraps to the tank to compensate for low tension in the already-installed wires. Furthermore, these prior art procedures involve a lack of engineering accuracy, which designers find quite undesirable.
In addition to the foregoing, there is always the possibility that a tank will be placed in service with undertensioned wires as a consequence of improper workmanship combined with mathematical errors.
It was in an effort to overcome these disadvantages of the invention is designed to operate on the ground and to travel numerous times around the periphery of the tank. For example, this machine may travel at a speed varying between a slow speed of 3 mph and a fast speed of 15 mph during the wrapping procedure.
This invention may involve a wheeled platform and a means for propelling it over the ground, this typically being a prime mover. Operatively mounted on the platform is a roll of wire representing the wire supply, a wire tensioning assembly, and a payoff wheel.
Of particular consequence to this invention is the utilization of a frame from which a weight of substantial size can be movably suspended for motion about an operating point. This weight serves in accordance with this invention as a tension indicating means and may in accordance with a principal embodiment of this invention, be suspended for vertical travel to an extent of approximately six feet, although if for some reason necessary, the weight could be arranged to travel up and down at an angle to the vertical.
In accordance with another embodiment of this invention, the weight may be mounted upon a balance beam. As will later be appreciated to a fuller extent, in each of these embodiments the weight is mounted for motion in a direction such that its position is influenced by gravity. The motion of the movably mounted weight serves in each embodiment as a reflection of the amount of tension in the wire and provides, during operation of the machine, a conspicuous indication, on a substantially continuous basis, of any changes in tension in the wire.
With regard to the principal embodiment of this invention, after the wire leaving the roll has been tensioned and before it gets to the tank, the path of the wire is deviated such that it passes around a suitable pulley, known as a wire deflection wheel. This pulley is operatively connected to the weight and is positioned on the apex of this deviation or deflection. It is usually preferable for the cable and pulleys that connect the weight to the wire deflection wheel be configured so that the weight will be equal to the desired tension of the wire. Therefore, if for example an 8 gauge wire is being installed on the tank, it would be typical to utilize a 3,000 pound weight therewith.
I am not to be limited to any one pulley arrangement, for in some instances it may be desirable to use a pulley arrangement such that the weight equals twice the tension in the wire, whereas in other instances the pulley arrangement may be such that the weight may equal two-thirds of the desired tension in the pulley.
It has been found convenient to create a weight of the proper size by the use of steel ingots, and to this end it is preferable to utilize a basket operatively attached to the aforementioned pulley, such as by the use of a relatively short cable. These ingots for example may be 41/2" square and 3' long, weighing approximately 200 pounds each. Therefore to create a 3,000 pound weight, 15 ingots may be stacked in the basket. These are approximate numbers, however, and the aggregate of all the ingots are weighed to obtain the desired weight.
Assuming for the moment that the wire being applied to the tank extends horizontally toward the tank, this wire passes over the pulley associated with the basket containing the ingots. With an increase in tension of the wire, this causes a force on the pulley, which in turn causes the weight to be lifted. Gravity acts in a favorable way in this instance inasmuch as in order for the weight to be lifted, there will need to be 3,000 pounds of tension in the wire. It is to be understood that in accordance with the above-described arrangement, a 3,000 pound weight will simply not be lifted if there is only 2,997 pounds of tension in the wire.
In the operation of this device, the operator adjusts the output of a pressure-applying device, such as a hydraulic pump or pneumatic pump so as to increase the tension in the wire via the slipbrake until the weight moves up from its lowermost position. When the preferred pulley arrangement is used, and when a 3,000 pound weight has been caused to move off of its resting position, there will necessarily be 3,000 pounds of tension in the wire. As the weight moves up and reaches a mid-point in the travel, known as the operating position, the operator continues to adjust the pressure-applying device, such as a hydraulic pump or a pneumatic pump until the weight reaches a steady-state condition in the mid position of its travel.
Instead of watching a gauge in accordance with the teachings of the prior art, the operator, in accordance with the principal embodiment of this invention, observes the position of the movably mounted weight. In order to keep the weight at or near its desired operating position, the operator either increases or decreases the pressure output of the hydraulic or pneumatic pump in order to keep the weight in a constant steady state condition.
If the weight goes up, this is because the tension in the wire has for one reason or another been increased. This fact will be immediately apparent to the operator, who will let off a little bit on the tension by manipulating a pressure relief valve associated with the hydraulic or pneumatic pump. This will cause the weight to drop down slightly and in this way the operator will be able to readily reestablish the desired operating position for the weight.
As long as a weight of carefully ascertained size is suspended at a steady state condition, the precise tension in the wire extending over to the tank is achieved. As should be obvious, this tension in the wire selected for a given set of conditions can easily be adjusted to a predetermined extent by merely adjusting the weight in the basket.
It is to be noted that certain problems necessarily occur with this type of wire wrapping, the most common of which involve bumps or irregularities in the road, with these serving, quite unfortunately, to affect the tension in the wire. An earthen roadway is the most economical roadway to use, but this type of roadway may get bumpy, particularly when the prime mover is traveling around the tank hundreds of times. One of the numerous advantages of the instant invention is that when an increase in wire tension occurs due to a bump, the weight raises to absorb the effect of this bump, with the tension in the wire remaining the same. Alternatively, if the effect of the bump was to cause a momentary lowering of the tension in the wire, then the weight would lower to absorb this fluctuation in the wire tension.
In accordance with this principal embodiment of the instant invention, the machine is configured such that the weight resides in a mid portion of a six foot travel, so as to provide the capability of three upward feet of travel as well as three feet of downward travel for the weight. This is an ample amount of travel in order for the weight to be able to absorb the deviations in wire tension caused by the bumps in the road. This highly advantageous arrangement is in stark contrast with the old technology mentioned hereinabove, wherein a bump in the road causes the tension in the wire to go up or to drop down abruptly, causing the tension in the wire on the wall to vary 5% to 10%.
Another factor to consider is that bumps in the road may be so sizable that the tension in the wire is increased to such an extent as to reach the breaking point of the wire. As previously mentioned, when the wire breaks, the wire that has lost its tension is not reusable, and such wire must be removed from the wall and discarded. This necessitates the wire winding operation to back up to the last point where proper tension exists in the wire remaining on the wall of the tank, where a clamp of a particular type was applied to cause the two ends of the wires to be clasped tightly together, thus to permit the wire wrapping to continue from that point.
It is quite significant to note that in accordance with this invention, if a bump is encountered in the road, this will not cause the wire to break, for the weight will advantageously raise to absorb this sudden increase in tension.
Another common problem encountered in wire wrapping is that the wire reel will on occasion hang up. That is to say it becomes momentarily hard to turn during the unreeling of the wire. This increases tension in the wire, and while using the techniques of the prior art, this can cause the wire to break. With the utilization of the instant invention, however, the weight will move upward to accept this momentary increase in tension in the wire. Sometimes the wire is really hung up and will not uncoil off the spool. While utilizing the techniques of the prior art, the wire will break inasmuch as the tension immediately runs up to the breaking point of the wire.
In accordance with the instant invention, however, the operator monitoring the vertical position of the weight is afforded a tangible period of reaction time which, although short, is usually sufficient for permitting the operator to stop the winding process prior to the wire actually breaking. It is thus to be seen that this new technology enables minor difficulties to be obviated during the uncoiling of the wire reel, and in many cases will provide the operator a sufficient amount of reaction tine for him to avoid the breaking of the wire.
Taking as an example an 8 gauge wire being tensioned over a length of 600 feet from zero tension to the optimum of 3,000 pounds of tension, is a known fact that this length of wire will stretch to an extent approximating three feet. In accordance with the just-described prior art procedure, it was necessary for the machine to be adjusted manually by the operator riding on the platform with his hand on the control of the pressure-applying pump, while looking at the position of the weight and adjusting the pump to maintain a constant position of the weight.
In accordance with another important embodiment of the instant invention, the problem of maintaining a consistent and proper tension in the wire may be handled automatically by virtue of limit switches provided at the upper end as well as the lower end of the path of travel of the weight. These switches are of course integrated into the electrical circuitry associated with this machine, and by way of example, these switches may be located 5 feet apart. The purpose of providing these limit switches is to automatically control the position of the suspended weight between the established limits of travel of the weight. As will be explained in detail hereinafter, this arrangement enables a highly effective automatic control of the tension in the wire.
As to the operation of this embodiment of my invention, when the weight is in the low position, indicating a lowered tension in the wire, it makes contact with the lower limit switch. This causes an electrical solenoid valve connected to the hydraulic or pneumatic pump to open and allow pressurized fluid to flow to the slipbrake, with the functioning of the slipbrake causing in this instance an increase in the tension of the wire. As the tension in the wire increases, the weight raises a relatively small distance, causing it to lose contact with the lower limit switch. This then causes a stoppage of flow of pressurized fluid to the slipbrake, which enables the vertical travel of the weight to stop and thus cause a constant tension to be maintained in the wire.
Conversely, if the weight makes contact with the upper limit switch, as a consequence of the tension in the wire increasing, the novel arrangement I utilize causes a different solenoid valve to open, with this particular valve permitting a flow of pressurized fluid out of the slipbrake, bringing about a reduction in tension in the wire and causing the weight to move down. As the weight drops slightly, contact is lost with the upper limit switch and the solenoid valve relieving the pressurized fluid from the slipbrake is reclosed, which reduces the downward travel of the weight, thus keeping the weight in suspension.
It has been found that in most instances the advantages associated with the automatically functioning of the instant machine outweigh the additional cost of implementing the above-described circuitry. The tension in the wire can, quite advantageously, be automatically controlled without the presence of an operator's full attention, with this of course serving to reduce labor costs.
I have ascertained that in the practice of the instant invention, the precise tension in the wire can be realized within less than 1% of the desired tension, which of course is a great improvement over the technology of the prior art. As previously mentioned, these earlier techniques permitted the tension in each individual wire to vary in excess of 10%.
It had earlier been mentioned that in accordance with another embodiment of this invention, the weight utilized for providing a conspicuous indication of wire tension may be mounted in a selectively movable manner upon a balance beam. As with the embodiments using a pulley-suspended weight, the weight utilized on a balance beam is mounted for motion in a direction such that its position is influenced by gravity. The motion of the movably mounted weight thus serves in each embodiment as a reflection of the amount of tension in the wire and provides, during operation of the machine, a conspicuous indication, on a substantially continuous basis, of any changes in tension in the wire.
As will hereinafter be described in considerable detail, the balance beam embodiment involves a low cost, low profile machine that makes possible the quick, precise adjustment of desired wire tension without the necessity of changing the size of the weight mounted on the balance beam.
It is therefore a primary object of this invention to provide a wire wrapping machine of minimal cost that will enable the tension in a wire being wrapped around a tank or other large structure to be maintained at a very precise value.
It is another object of this invention to provide a wire wrapping machine that will enable uniform tension to be realized in each wrap of wire around a tank or other large structure while at the same time minimizing labor costs.
It is still another object of this invention to provide a wire wrapping machine having means enabling in a non-complex manner the tension in each wrap of a wire around a large structure to be readily and accurately adjusted to meet precise design requirements.
It is yet another object of this invention to provide a wire wrapping machine that despite its relatively low cost will nevertheless enable a precisely accurate tension to be maintained in the wire being wrapped around the large structure, thus obviating the need for stopping the wrapping procedure from time to time in order to check the precise tension in the wire already applied to the structure, and to compare that tension with a gauge reading.
It is yet still another object of this invention to provide an economically produced wire wrapping machine that is able to wrap wire on a large structure so accurately to a preestablished value of tension that it becomes unnecessary to apply an additional wrap upon the structure, to make up for the fact that the already-applied wire might have been wrapped on the structure at an inadequate tension.
It is a further object of this invention to provide a wire wrapping machine that can demonstrably wrap a large structure to a high degree of accuracy, thus to prove to designers and inspectors alike that wire is being wrapped on a large structure to an entirely adequate degree of tension.
It is a yet further object of this invention to provide a wire wrapping machine having the ability to absorb sudden increases in wire tension, thus to give the operator increased reaction time in which to stop the machine should a problem threatening wire breakage unexpectedly occur.
It is a still further object of this invention to provide a wire wrapping machine utilizing a large weight maintained in suspension and capable of limited vertical movement, with the amount of tension in the wire being wrapped about the tank affecting the vertical positioning of the weight and being consistent with the mass of the weight, with changes taking place in the height of the weight used in accordance with the principal embodiment from a mid position during the wrapping procedure representing a conspicuous indication to the operator of changes occurring in the tension of the wire being wrapped.
It is another object of this invention to provide a wire wrapping machine that is automatic in operation and advantageously not requiring a full time operator.
It is still another object of this invention to provide a balance beam alternative to the weight suspended by means of a pulley arrangement, with the balance beam embodiment making possible the easy, quick and precise adjustment of desired wire tension without necessitating a change in the size of the weight being utilized.
It is yet still another object of my invention to provide a balance beam embodiment wherein the position of the weight slidably mounted on the balance beam can be easily and precisely adjusted by the operator, thus to readily enable a selected wire tension to be achieved, with this embodiment also providing the advantage of a low profile machine.
These and other objects, features and advantages will be more apparent as the description proceeds.